(1) Field of the Invention
The present invention relates to a multiplex writing implement, and more detailedly to a multiplex writing implement having a plurality of writing elements selected from any combination of the following writing elements:--normal oil-based ball-point elements; ball-point writing elements which are filled up with so-called thixotropic water-soluble or low-viscosity oil-based ball-point ink; mechanical pencil elements; etc.
(2) Description of the Prior Art
A ball-point pen is typically composed of a point assembly consisting of a ball and a tip holder, an ink reservoir, a pen barrel, etc. In writing with the ball-point pen, when the ball as a writing point is rotated, ink flows out from the point assembly and is transferred to or infiltrated to a recording medium such as paper etc., whereby line traces as well as drawn lines are formed by the transfer.
Since water-type ball-point pens use an ink which has a low viscosity of some mPa S or less, the ball-point pens of this kind offer an advantage to the user, namely the user does not need to press hard and can write comfortably. Ball-point pens of this kind, however, surfer from some drawbacks, such as the forward leakage phenomenon, the back leakage phenomenon, etc. The former phenomenon causes the ink to ooze out from the writing point, whilst the latter phenomenon is caused by air entering the point assembly via writing point, inducing the ink to flow out backwards. These phenomena can be prevented by using a piece of fabric called `tampon`. On the other hand, if the ball-point pen is left with its cap off, the vapor pressure of the solvent will increase causing the solvent to evaporate. Therefore, there is a concern that the writing point might dry up, causing a lack of ink flow thereby prohibiting writing.
Meanwhile, since conventionally known oil-based ball-point pens use an ink having a viscosity of some thousands mPa S or more, a considerably large friction arises when the ball rolls and the ink flows out from the writing point. Therefore, there is a concern that the conventional oil-based pen can not provide a smooth writing sensation. Further, in the conventional oil-based pen at times an insufficient amount of ink flows from the writing point during writing and at others too much leaks out causing blobbing. Therefore, the conventional oil pen suffers from defects, namely that lines drawn in parts may be irregular, the density of the written trace may be light, or a strong pressure for writing may be needed to be exerted.
For these reasons, recently, a ball-point pen for water-soluble ink which has a viscosity half way between that of the above water-soluble type and the oil type (ranging from some mPa S to some thousands mPa S), has been developed for the improvement of the oil-based ball-point pen. This ball-point pen uses water-soluble ink that presents a relatively low viscosity and has so-called thixotropy. Thixotropy is the characteristic which lowers the viscosity of ink as the tip ball rolls during writing, thus allowing smooth distribution of ink. This type of ball-point pen, however, has the defect that the ink tends to dry up; therefore, it normally needs a cap which is able to seal off the tip part of the writing element. Additionally, since the amount of the ink flowing out will increase, it is also necessary to make the ink reservoir greater in diameter to hold a larger quantity of ink, in order to increase its life of writing.
As the improvement of the oil-based ball-point pen, it is possible to also consider a ball-point pen which uses an oil-based ink which has both a low viscosity and an excellent dryout-resistance. But a ball-point pen of this type, still has the problem that a large amount of ink flows out. Again, in this case, it is necessary to make the ink reservoir greater in diameter to hold a greater quantity of ink, in order to increase its life. Moreover, since the viscosity of the ink is low, when the tip is placed down and a gap is created between the tip ball and the tip holding portion, forward leakage of ink occurs, thus ink oozes out.
That is, since the water-soluble ink having a medium viscosity and the low-viscosity oil-based ink both have a relativity low viscosity, this tends to cause back leakage or forward leakage of ink. If the back or forward leakage of ink occurs, the ink may stain clothes etc. Further, another defect may occur in which, due to impacts from being dropped or clicking, the ink will become clogged causing ink-starving in writing.
For the ball-point pen with a medium-viscosity water-soluble ink, a translucent, nondrying greasy material called `follower` is usually filled at the rear end of the ink reservoir. Therefore, when trying to prevent ink evaporation, it is enough to consider the reduction of ink due to the evaporation from the gap between the writing point or the ball and its holder. Therefore, if, for example, a solvent having a considerably low vapor pressure is mainly used as in the oil-based ball-point pen, it is not necessary to consider the evaporation of ink. In the case of the water-soluble ink, however, the main component of the solvent is water; therefore the use of a low vapor pressure solvent can not prevent water from evaporating.
Meanwhile, an ink has been known which can be erased by a rubber eraser. This ink uses the difference in solubility of rubber component in the ink solvent. That is, the ink will be a gel inside the ink reservoir while it will become a sol when the tip ball rolls during writing. The ink will again become a gel when the ink is drawn on the writing surface, so that the ink will not be absorbed into the paper.
There is a known writing implement called a multiplex writing implement, which has a plurality of writing elements such as a mechanical pencil and a ball-point pen etc., and which selectively allows either of the elements to come in and out at the front end thereof. Various kinds of the mechanisms for achieving the writing elements to be projected and retracted at the front end of the multiplex writing implement, have been known. Examples of the mechanisms include a clicking type, a slider type in which sliders exposed to the outside from the side of the barrel cylinder of the writing implement should alternately be slid, a cam type in which a cam cylinder having a slope is rotated to achieve the function, etc.
Known examples of the multiplex writing implement of this kind, include a configuration in which a plurality of normal-type oil-based ball-point writing elements are pushed out. This implement is constructed so that the writing elements fixed to corresponding click-operating portions inside the barrel cylinder are slidably provided along corresponding length-wise grooves formed inside the barrel cylinder, and when one of the tip portions of the writing elements is selectively projected out from the front end opening of the barrel cylinder and engaged in place, the engagement of the other writing element is released so that the disengaged writing element is retracted into the inside of the barrel cylinder by the action of the return spring.
In the multiplex writing implement of this kind, when one of the writing elements is selected so that the tip portion of the selected element is projected out from the front end opening of the front barrel, the click-operating portion will be engaged in a flexed state with respect to the axial direction. Therefore, the writing element, if it is non-flexible, will not achieve the necessary function. Particularly, consider a case where a ball-point pen having a water-soluble medium-viscosity ink or oil-based low-viscosity ink is used as a writing element of the multiplex writing implement. In this case, since the ink reservoir needs to be of a greater diameter as stated above, it is impossible to create a sufficiently large margin between the writing elements, unlike in the configuration in which the regular-diametric writing elements were used. Therefore, the tip part of the writing element to be projected can not be guided smoothly to the center of the front end opening of the barrel cylinder. That is, the movement of the writing elements is impeded, and consequently, the tip parts of the writing elements could be disallowed from either projecting or retracting. For the large-diametric writing elements to be projected or retracted, the diameter of the barrel cylinder may be made very large. This, however, gives rise to a problem of deteriorating the portableness and handling performance of the writing implement.
As stated above, since the projecting/retracting mechanism of the conventional multiplex writing implement incorporates return springs for retracting writing elements into the barrel cylinder, it has a complicated structure needing an increased number of parts and resulting in an increased cost. Additionally, the conventional mechanism requires a large space, this means that there is dimensionally little space for the writing elements.
The conventional multiplex implement suffers from other drawbacks such as it will stain clothes if the writing implement is placed in a breast pocket etc. with its writing point projected out.
Publicly known technologies relating to the multiplex writing implement of the invention include those disclosed in Japanese Patent Application Laid-Open Hei 7 No.214,986, Japanese Patent Application Laid-Open Hei 6 No.328,891, Japanese Utility Model Application Laid-Open Hei 6 No.53,185, Japanese Utility Model Application Laid-Open Hei 7 No.33,680 and Japanese Utility Model Publication Hei 3 No.35,589.